This invention relates to sheet material such as negotiable instruments, currency or other documents having critical numerical data as currency values, serial numbers and the like on the face thereof. Commercial paper in the form of checks, bank drafts and the like represent a large portion of the sheet material to which this invention pertains.
More particularly, the invention relates to a security device imprinted upon sheet material and a method of marking the device to insure the integrity of the paper when processed through automatic scanning or accounting machinery.